Carbon/graphite is commonly used as the heating element in various heating devices and/or as a part of electrodes because it is electrically conductive, anti-static, capable of dispersing electrical current evenly throughout the entire heating element, environmentally safe, inexpensive, and relatively easy to handle (e.g., Ellis, U.S. Pat. No. 3,999,040, Dec. 21, 1976; Klaus & Quick, U.S. Pat. No. 4,534,886, Aug. 13, 1985; Goldsmith et al., U.S. Pat. No. 4,586,999, May 6, 1986; Takeda, U.S. Pat. No. 4,783,586, Nov. 8, 1988; Barker et al., U.S. Pat. No. 5,851,504, Dec. 22, 1998: Kochman et al., U.S. Pat. No. 6,452,138, Sep. 17, 2002; Calver et al., U.S. Pat. No. 6,511,767 B1, Jan. 28, 2003; Baca et al., U.S. Pat. No. 7,933,114 B2, Apr. 26, 2011; and Harutyunyan et al., U.S. Pat. No. 8,124,043 B2, Feb. 28, 2012). When a carbonic material is mixed with water-based poly-acrylate, polyurethane, or polyethylene emulsion and is coated or laminated on non-woven fabric, fiberglass panel, plastic panel, or plywood, it results in a warm temperature heating pad within a range of 20°-50° C., which is suitable for keeping human bodies and pets warm (i.e., Lee et al., U.S. 61/743,556, Sep. 7, 2012).
If a heating device is going to be used for construction and industrial purposes such as heating panels, heating boards, space heaters, hanging heaters, and industrial dehydrators, it needs to achieve a higher surface heat generating capability. A manufacturer may increase the surface temperature of a conventional carbon-based heating device by: (a) introducing a higher electrical voltage to the heating element, (b) increasing the carbon content in the heating element, (c) using a metallic rather than non-metallic base layer coated with carbon, (d) shortening the distance between positive (+) and negative (−) electrodes on a heating element, and (e) adopting any combination of all the above options. The problem with any of these options is that, as the temperature raises to a level of 140° C. or higher, all the organic materials such as organic carbon, non-woven fabric, and plywood tend to oxidize, burn, smell, and cause environmental hazards.
In order to solve the above problem, this invention introduces fire retardant chemical compounds such as sodium silicate, aluminum silicate, aluminum hydroxide, sodium hydroxide, sodium colloidal silica, sodium sulfate, and other flame deterrents. Among these materials, the suitable choices include sodium silicate and aluminum silicate. Sodium silicate (Na2SiO3) is commonly known as water glass or liquid glass and has a number of desirable characteristics that can be beneficial for building construction materials, such as being fire resistant, high temperature adhesive, bonding/sealing capability, electrically conductive at a low level, anti-corrosive, and others. Additionally, it is inexpensive. Because of these unique properties, it has been widely used in manufacturing fire retardant and/or insulating materials (e.g, Cook, U.S. Pat. No. 4,015,386, Apr. 5, 1977; McLaren, U.S. Pat. No. 4,196,242, Apr. 1, 1980; Kai & Majors, U.S. Pat. No. 7,279,437 B2, Oct. 9, 2007; Majors, U.S. Pat. No. 7,655,580 B2, Feb. 2, 2010; Chick, Patent Application US 2011/0192539 A1, Aug. 11, 2011; Kipp et al., Patent Application US 2012/0148831 A1, June, 2012); anti-corrosive materials (Boffardi, U.S. Pat. No. 5,232,629, Aug. 3, 1993; Pratt, U.S. Pat. No. 5,756,160, May 26, 1998), water proofing concrete and masonry treatments (e.g., Sanchez, U.S. Pat. No. 5,112,405, May 12, 1992); and others. Aluminum silicate (Al2Sio3) is also inexpensive, electrically conductive, flame deterrent, and a waterproofing agent. As a result, it is often used as a heat absorption agent in temperature control devices (e.g., Hayes, U.S. Pat. No. 6,241,909 B1, Jun. 5, 2001; Erick et al., Patent EP 2038221 A2, Mar. 5, 2009).
While sodium silicate is widely used as fire retardant/insulation materials, its use in conjunction with carbon-based heating devices has not been previously appreciated. Even when these two materials are utilized jointly, the main focus of their uses has been on controlling carbon steel corrosion (Boffardi, U.S. Pat. No. 5,232,629, Aug. 3, 1993), protecting carbon composite materials on their surface (Pratt, U.S. Pat. No. 5,756,160, May 26, 1998), or reinforcing tire tread rubber compositions (Agostini et al., U.S. Pat. No. 6,667,353 B2, Dec. 23, 2003) in non-heating devices manufacturing industries. One possible reason may be that because sodium silicate is easily soluble in water, any finished product containing it can be easily water damaged. To deal with this possibility, this invention mixes sodium silicate with aluminum silicate or aluminum hydroxide. Aluminum silicate not only has heat absorption capability but also has coagulating capability. As such, it is often used as a waterproofing agent in construction industries.
This invention is intended to capitalize on the synergistic effect of graphite and sodium silicate in constructing heating devices. As discussed earlier, a problem of constructing a high temperature carbon-based heating device is that as it rises, the heating device tends to oxidize, burn, smell, and cause environmental hazards. In order to deal with this problem, this invention mixes graphite with sodium silicate to produce a fire resistant coating agent and coat or laminate it on the surface of an organic base layer material made of non-woven fabric, paper, or plywood for constructing moderate surface temperature heating boards (50°-120° C.) and on the surface of an inorganic base layer material made of cement, ceramic, fiberglass, plaster, or metal for high temperature heating boards (120°-250° C.). Such fire resistant heating devices do not burn and/or disintegrate at 250° C., which makes them excellent building materials.
Sodium silicate generally bonds well with most surface materials. In order to enhance the bonding quality, however, this invention uses inorganic graphite carbon rather than organic carbon source to mix it with inorganic sodium silicate. Because the chemical properties of inorganic graphite and inorganic sodium silicate are harmonious, they tend to bond naturally. Additionally, since sodium silicate is a high temperature adhesive, the coating agent that is composed of graphite and sodium silicate tends to bond well with any surface material including plywood, fiberglass, plaster board, cement and any road payment materials. This graphite-sodium silicate coating agent is an excellent source of materials for constructing heating devices with fire retardant capability.
In the embodiments of this invention, the surface temperature of heating devices can be controlled by: (a) changing the electrical voltage, (b) changing the composition of the coating agent (graphite-sodium silicate mix), (c) changing the thickness of the coating agent, (d) changing the length of the heating element, (e) adjusting the distance between positive (+) and negative (−) electrical wires placed on electrodes, and/or (f) changing the base layer of heating devices—non-woven fabric, plastic panel, plywood, plaster board, and metallic panel. Table 1 shows different compositions of heating devices at different temperature levels—warm, moderately, and high temperature.
TABLE 1Differing Compositions of Heating DevicesSurface Temperature20°-50° C.50°-120° C.120°-240° C.Electrical voltage120 V120/240 V240 VCarbon typeOrganicInorganicInorganicChemical mixPoly acrylicSodium silicate/Sodium silicate/emulsionAluminum silicateAluminum silicateBase layer materialOrganicOrganic/InorganicInorganicThickness of coating0.5-0.8 mm0.5-1.00 mm1.0-1.3 mmLength of heating elementLongerLonger/ShorterShorterDistance between + & − electrodes LongerLonger/ShorterShorter
As shown in Table 1, if a warm temperature heating device (20°-50° C.) is needed, the manufacturer may: (a) use a 120 volt electrical current, (b) use an organic carbon powder in the coating agent, (c) mix the organic carbon with water-based poly acrylic emulsion, (d) use an organic base layer such as non-woven fabric and plywood, (e) make the coating agent thinner on the heating element, (e) lengthen the size of the heating element, and/or (f) keep the distance between positive and negative electrical wires/electrodes longer. On the other hand, if a high temperature heating device (120°-250° C.) is needed, the manufacturer may: (a) use a 240 volts of electrical current, (b) use an inorganic graphite carbon in the coating agent, (c) use an inorganic base layer such as cement, ceramic, plaster, fiberglass and metal plate, (d) mix graphite with sodium silicate, (e) make the coating agent thicker on the heating element, (f) shorten the length of the heating element, and/or (f) shorten the distance between positive and negative electrical wires/electrodes. Moderately high temperature heating devices (50°-120°) need the mid-range options. Warm temperature (20°-50° C.) heating devices are basically used to keep human bodies or animals warm. Moderately high (50°-120° C.) to high temperature (120°-240° C.) heating devices can be used to construct heating panels/boards, hanging heaters, space heaters, industrial dehydrators, and others.
The main benefit of such heating devices is that they can cut the electric heating bills substantially. Conventionally, the entire house is heated by a centralized electrical heating, gas burning, or oil burning system. Unlike the centralized heating system, the graphite-sodium silicate based heating devices can be locally installed to heat the rooms in a house where heat is needed. For example, heating wall boards and/or heating floor mats can be permanently installed in frequently used rooms, while space heaters and/or wall hanging heaters can be utilized in infrequently used rooms. Or, the space heating heaters can be used in conjunction with a conventionally centralized heating system by placing them in rooms where an additional heat is needed. Such a strategic installment of graphite-sodium silicate based heating system is likely to reduce heating costs substantially. Additionally, an important benefit is that because the graphite-sodium silicate coating agent is electrically conductive, it naturally becomes an anti-static agent. So, the graphite-sodium based heating devices can be installed to heat buildings that require anti-static building materials. Consumer electronics, chemical, pharmaceutical, and military installations dealing ammunitions are such industries.
How safe are graphite, sodium silicate, and aluminum silicate? These materials have been around in the natural environment for many years without causing serious environmental and health risks. However, if graphite, sodium silicate, and/or aluminum silicate powders are/is inhaled, it can cause some irritation in the respiratory track and/or cause some damage in the lung and in the digestive system. Moreover, sodium silicate is essentially a strong alkaline that is harmful to human bodies. Alkaline is needed to neutralize acid in our body, but too much of it poses health risk. Also, if sodium silicate solution is touched, it can irritate the skin and eyes. Thus, people who handle these chemical compounds need to wear protective equipment such as gloves, goggles, and lab coat. A plant handling these chemicals needs to be well ventilated to dust off the chemical. Once they are mixed, the mix is coated on the base layer, and surface is dried, much of the health risk is neutralized. That means, the finished products are fire resistant, environmentally safe and seem to present no health risk.
The core of graphite-sodium silicate (G-S) based heating devices is an environmentally safe, fire retardant, and economically viable a graphite-sodium silicate (G-S) coating agent that can be coated on an organic or inorganic base board. Since we are aiming at constructing a variety of G-S based heating devices for personal and industrial uses, it would be desirable to develop a set of coating agents that are independently and collectively capable of generating a desired surface temperature for heating devices without causing fire hazard, health risk, and or material disintegration. Developing such coating agents is the main focus of the present CIP report.